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Copper oxide nanopowder modified carbon paste electrode for the voltammetric assay of vonoprazan
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Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Vonoprazan (VPZ) is a novel promising member of gastric acid-suppressive medicinal administrated in Japan in 2015. Only a few HPLC analysis protocols were reported for VPZ assaying, therefore, the present work describes for the first time a novel copper oxide nanoparticles-based sensor as a promising analytical tool for differential pulse voltammetric determination of vonoprazan with enhanced sensitivity compared with the bare electrode. An irreversible oxidation process with the two-electron transfer was elucidated with scan rate measurements. At the optimized conditions, peak heights showed against VPZ in the concentration range from 0.99 to 20.00 µg mL−1, and detection limit of 0.24 µg mL−1. The proposed sensor showed prolonged stability with a 95% recovery of the original peak height within the first 30 days. Good reproducibility and repeatability of the fabrication protocol was reported with RSD 1.3%. Noticeable resolution between the VPZ, ascorbic acid, and uric voltammetric peaks allows accurate assaying of VPZ in biological fluids with average recoveries agreeable with the conventional HPLC techniques.
Keywords
Vonoprazan
Differential pulse voltammetry
Carbon paste electrode
Copper oxide nanoparticles
1 Introduction
Peptic ulcer is considered as the most serious and the predominant gastrointestinal disease over the world (Azlina & Aishah, 2020; Adinortey et al., 2013). Helicobacter pylori infection represents the major reasons of inveterate gastritis, peptic ulcers and gastric tumor (Pereira & Medeiros, 2014). Administration of new effective treatment for infection of H. pylori represents a very challenging goal. A combination of antibiotics and a proton pump inhibitor (PPI) is the first-line therapy for H. pylori (Chey et al., 2017). Acidic instability, sluggish action, and poor nighttime performance were all drawbacks of the typical proton pump inhibitor (Oshima & Miwa, 2018). As a consequence, to treat H. pylori infection, a more powerful inhibitor for proton pump, is needed. Vonoprazan, (VPZ; 1-(5-(2-fluorophenyl)-1-(pyridin-3-ylsulfonyl)-1H–pyrrol-3-yl)-N-methyl-methanamine) is novel oral potassium-competitive acid blocker which reversibly inhibits the gastric hydrogen potassium ATPase with the advances of a rapid and long-lasting action (Graham & Dore, 2018). VPZ succeeded to overcome many of the perceived traditional proton weakness with a noticeable inhibition potency about 350 times higher compared with the most common PPI lansoprazole and a more favorable safety profile (Echizen, 2016; Ashida et al., 2015). Because of its acid-resistant features, VPZ induced acidity up to 24 h via condensation inside acidic canaliculi of cells belong gastric parietal (Hori et al., 2010). (pKa 9.37). VPZ expanded the intragastric pH above 4.0 in 4 h, and its anti-secretory ongoing transition for 24 h. As novel PPIs available since February 2015 (Garnock-Jones, 2015), the literature survey showed limited methods for VPZ assay. Only chromatographic protocols were reported in the literature for VPZ analysis. To identify seven impurities in VPZ pharmaceutical formulations, chromatographic method with mass spectrometric detector was performed (Liu et al., 2016). A liquid chromatographic strategy via a reversed-phase was applied to measure VPZ and its degradants in bulk drug formulation (Luo et al., 2018). A mass spectrophotometric protocol combining liquid chromatography and tandem mass spectrometry was developed to evaluate the metabolites of VPZ in plasma (Yoneyama et al., 2016). Qiao (Qiao et al., 2017) developed and validated a sensitive liquid chromatographic protocol for measuring VPZ pyroglutamate derivatives in biological fluids. The process cited was thought to be used to investigate the bioequivalence of VPZ pyroglutamate and fumarate. The chromatographic analysis protocols described above were time-consuming, costly, and unsuitable for simultaneous estimation of impurities in organic solvents. VPZ is not yet official in any pharmacopeia; therefore, the development of a simple, sensitive, and effective analysis protocol for quantification of VPZ is welcomed. The electrochemical technique enables the screening of one or more active drugs in the same run with improved sensitivity applying simple instrumentation and sample pretreatment steps. Electroanalytical frameworks have been suggested as useful methods for evaluating pharmaceutical compounds in biological samples and bulk formulations (Ozkan, 2012; Siddiqui et al., 2017; Angnes, 2015; Ozkan et al., 2015; Ziyatdinova & Budnikov, 2015).
At least since the nineties of the last century, Vytras group motivated the fabrication and application of carbon paste electrodes (CPEs) in voltammetric analysis (Svancara et al., 2019; Švancara et al., 2001; Švancara et al., 2009). CPEs are a heterogeneous matrix composed of a conductive carbon powder with a suitable liquid binder which is pressed into a piton like holder with an electric contact. The most promising future of these working sensors is the possibility of bulk modification and simple regeneration of the electrode surface through polishing with wet filter paper. Carbon paste electrodes found sounding publications in electroanalytical field (Švancara et al., 2001; Švancara et al., 2009; Manjunatha et al., 2012; Manjunatha, 2018; Chandrashekar et al., 2010; Manjunatha, 2017; Manjunatha et al., 2013; Shankar et al., 2010).
Herein, for the first time, differential pulse voltammetry (DPV) for assaying VPZ was reported using working carbon paste electrodes integrated with copper oxide nanoparticles. The proposed sensors showed promising futures including simple fabrication and regeneration protocols enhanced reproducibility and stability. The enhanced selectivity and sensitivity of the fabricated sensors suggesting their application for voltammetric assay of VPZ in pharmaceutical and biological samples compared with the conventional HPLC techniques.
2 Experimental
2.1 Reagents and chemicals
Paraffin oil (PO, Merk) and synthetic graphite powder (Aldrich) were used for fabrication of the carbon paste working electrode. Modification of the electrode was performed using copper oxide nanopowder (Alfa Aesar, 30–50 nm). Sodium dodecyl sulphate (SDS, Fluka) was used. The universal buffer (4.0 × 10−2 mol L−1) was prepared as usual where the desired pH value was adjusted with sodium hydroxide.
2.2 Drug substance
VPZ fumarate stock solution was prepared by dissolving 0.01 g standard VPZ (C17H16FN3O2S.C4H4O4, 461.46 g mol−1 with a purity of 99.25 ± 1.2%, National Organization for Drug Control and Research, Egypt) in 25 mL bidistilled water and kept at 4 °C.
2.3 Biological samples
Fresh serum samples received from healthy individuals were centrifuged at 2500 rpm for 5 min, and spiked with different VPZ concentrations. Acetonitrile (with ratio 2:1) was added to the sample for precipitation of serum protein, and the sample was diluted up to 10 mL with doubly distilled water. The samples were vortexed and centrifuged followed by filtration to remove the residual protein. Urine samples were spiked with standard VPZ solution and treated with methanol to remove protein. The VPZ amount in the clear upper layer was measured voltammetrically in addition to chromatographic analysis with UV detection at 230 nm (Luo et al., 2018).
2.4 Apparatus
Metrohm voltammetric analyzer (797 VA, Metrohm, Switzerland) was used for voltammetric measurements. Unmodified carbon paste working electrode was fabricated by blending 80 µL paraffin oil as pasting liquid with 0.2 g of graphite powder and the result paste were packed in a piston like Teflon holder (Svancara et al., 2019). Electrode modification takes place through replacing 5.0% of the carbon powder with copper oxide nanoparticles and the paste was prepared in the same manner. The electrode surface was regenerated simply using a wet filter paper. Silver/silver chloride and platinum wire (Metrohm) were used as reference and auxiliary electrodes, respectively.
2.5 Procedures
At the optimum pH, increments of the fresh VPZ solution were applied to a supporting electrolyte containing 200 µL of 1.0 × 10−3 mol L−1 SDS. The scan rate was 40 mV s−1, the pulse height was 50 mV, the pulse width was 100 ms, and the pulse duration was 40 ms for the differential pulse voltammograms. In a µg mL−1 scale, the peak current (µA) was plotted against the VPZ concentration.
3 Results and discussion
3.1 Voltammetric behavior of VPZ
As a novel pharmaceutical compound, no reported work describing the electrochemical behavior of VPZ were found in literature. Metal oxides with their nanostructures showed a promising electrocatalytic effect towards oxidation of pharmaceutical compounds offering sensitive and elective voltammetric approaches for detection of many pharmaceutical formulations (Agnihotri et al., 2021; Qian et al., 2021; Abdel-Raoof et al., 2020a; Abdel-Raoof et al., 2020b; 29-32, Khoobi et al., 2014; Mosleh et al., 2018; Hendawy et al., 2019; Azab & Fekry, 2017; Fekry, 2017). Therefore, the electrochemical features of VPZ were explored on the bare carbon pate electrodes and those incorporated with copper oxide nanopowder (Fig. 1). Applying bare carbon paste electrode, VPZ showed a single anodic oxidation peak at 1.02 V with no peaks in the cathodic direction assuming the irreversibility of VPZ oxidation at the electrode surface. Modification of the electrode matrix with copper oxide nanostructure improved the peak current by about 5 folds for 5% CuO. From different modifier contents, 5.0% was selected (Fig. 1). It is noteworthy to mention that the VPZ peak on the electrode surface was diminished by successive measurements which may be attributed to adsorption of the VPZ oxidation products at the electrode surface. Addition of sodium dodecyl sulphate (SDS) to the supporting electrolyte improved the peak current and maintained the VPZ oxidation peak (Fig. 1).
Cyclic voltammograms for 4.82 µg mL−1 VPZ recorded on CuO based carbon paste electrode in BR buffer containing 1.3 × 10−5 mol L−1 SDS at pH 6.0. Scan rate was 40 mV s−1.
The electroactive surface area of the working electrode was explored by recording the peak current fericyanide as a redox prob at different scan rate values. According to Randles-Sevik equation, the electroactive surface area of the bare carbon paste electrode was 0.025 compared with 0.155 cm2 for 5.0% CuO bulk modified electrodes (Zhang & Wang, 2000).
3.2 pH-effect on the electrochemical behavior of VPZ
Based on its chemical structure, VPZ showed apparent pKa values were 4.6 and 9.3, respectively (Liu et al., 2016; Scott et al., 2015; Yang et al., 2018; Shin et al., 2011). VPZ is unstable in base condition; therefore the pH influenced its electrochemical behavior. The peak height gradually increased with pH and conducted to extreme value at pH 6.0. At higher pH values the peak performance was diminished, therefore, the pH 6.0 will be selected for the proceeding studies. This optimum pH value agreed with those used for mobile phase in chromatographic methods for VPZ (Liu et al., 2016; Scott et al., 2015). Moreover, the peak potentials were shifted towards the negative direction with non Nernstian compliance (Ep = 1.1049–0.0282 pH, r = 0.9995). This slope value sustained the involvement of unequal number protons and electrons in the oxidation reaction and the rule of proton in the oxidation of VPZ (see Fig. 2).
(a) DPV of 4.82 µg mL−1 VPZ in BR buffer containing 1.3 × 10−5 mol L−1 SDS at different pH values; (b) pH effect on the VPZ peak current and potential. Scan rate was 0.040 V s−1.
3.3 Voltammetric activity at various scan rates.
Cyclic voltammograms were measured at various scan rates ranging from 20 to 220 mV s−1 to illustrate the oxidation mechanism of VPZ at the electrode surface (Fig. 3a). Improving the peak current linearly (r = 0.9961), according to scan rate's square root. (ν1/2), indicates diffusion-controlled oxidation mechanism at the electrode surface (Fig. 3 b). Draw a relation between log value of the current peak log (I/µA) and the log san rate log (υ/Vs−1) which yields a linear relationship with a slope of 0.5928 that verifying diffusion-controlled reactivity (Fig. 3c). Increasing the san rate values resulted in shifting of the oxidation peak potentials to more positive values (Fig. 3d) which sustain the irreversibility of the VPZ oxidation at the electrode surface (Zhang & Wang, 2000; Elgrishi et al., 2018). Moreover, the peak potential showed linear relationship against the log υ (E (V) = 1.06085 + 0.05441 log (ʋ/Vs−1)). The number of electrons involved in the oxidation of VPZ was calculated to be 2.188 (Laviron, 1972).
VPZ voltammetric activity at various scan rates on the CuO/CPE surface at pH 6.0.
Consequently, the irreversible electrochemical oxidation of VPZ takes place through oxidation of the terminal amino group via transferring of two electrons with the liberation of one proton and formation of double bond (scheme 1).
Computed reaction mechanism for electrochemical oxidation behavior of VPZ at CuO/CPE surface.
3.4 Analytical characterizations
At the optimized measuring conditions, 19-successive increments of VPZ standard solution were added to the supporting electrolyte with that the final concentration ranged from 0.99 to 20.00 µg mL−1. The peak current of the recorded for voltammograms of differential pulse, were plotted against the VPZ concentrations in µg mL−1 scale (Table 1 & Fig. 4). The obtained calibration graph showed high linear correlation coefficient and low standard deviation values confirming the good linearity and the applicability of the proposed analysis protocol within the selected VPZ concentration.
Parameters
Linear range (µg mL−1)
0.99–20.00
Slope (a) (μAcm−2)
0.310
sa (μAcm−2)
0.002
Intercept (b) (μA mL µg)
0.130
sb (μA mL µg)
0.020
Sy/x (µA cm−2 mL µg)
0.154
Correlation coefficient (r)
0.9997
r2
0.9994
LOD (µg mL−1)
0.24
LOQ (µg mL−1)
0.72
RSD %
0.94
N
19
Intra-day repeatability (RSD%)
0.57
Inter-day repeatability (RSD%)
0.652
Electrode stability after 4 weeks (RSD%)
0.612
Within-day reproducibility
0.782
Between days reproducibility (RSD %)
0.857
Voltammetric determination of VPZ at CuO/CPE in BR buffer containing 1.3 × 10−5 mol L−1 SDS at pH 6.0. 0.040 V s−1 was the value of scan.
3.5 Stability and reproducibility of measurement
The performance stability of the fabricated copper oxide nanoparticles modified carbon paste electrode was performed over a prolonged time period by recording the differential pulse voltammograms in presence of 4.82 µg mL−1 VPZ. The proposed sensors showed stable oxidation peak currents within the first 30 days with RSD 0.612% with a 95% recovery of the original peak height. With prolonged storage, the sensor performance started to deteriorate slowly (about 10%). Successive replicate measurements for 4.82 µg mL−1 VPZ with the same electrode surface showed intra-day repeatability with RSD 0.57%.
One of the most promising futures of CPE is the ease regeneration through polishing with a filter paper (Svancara et al., 2012). Herein, regeneration of the electrode surface resulted in complete recovering of the peak height and removing the memory effect of the electrode. The reproducibility of the electrode fabrication process was estimated through recording the DPV response for five different fabricated sensors towards VPZ. Acceptable RSD of 1.3% was achieved confirming the good reproducibility and repeatability of the fabrication protocol sensors.
3.6 Interference studies
VPZ appeared to be resistant to thermal, acidic, and photolysis upon exposure to alkaline oxidative stress conditions (Liu et al., 2012). Due to the elimination of the electroactive amino group, none of the identified degradation products are anticipated to interfere with the voltammetric calculation, so the proposed analysis methodology can be used to ensure the consistency of VPZ in pharmaceutical formulations.
Contaminates and excipients are usually present in biological samples and dosage forms; therefore, the interference studies are quite crucial. The selectivity of the presented copper oxide nanoparticles-based sensor was investigated toward VPZ in existence of common excipients, additives, and biomolecules.
In the existence of uric acid (UA), ascorbic acid (AA), and other excipients commonly found in pharmaceutical formulations such as glucose, starch, and citric acid, a differential voltammograms for 4.82 µg mL−1 VPZ were reported. In BR buffer pH 6.0, sequential evaluation of AA, UA, and VPZ is shown in Fig. 5. With 97.14% recovery of the VPZ peak and a high tolerance limit, sharp and sensitive peaks were correlated with high resolution (0.53 V between VPZ and UA).
Synchronous voltammetric measurement of VPZ in existence of uric acid and ascorbic acid by using CuO/CPE at pH 6.0.
Metabolism of VPZ to inefficient metabolites basically achieved by CYP3A4 with minor participation of sulfotransferase 2A1, CYP2C9, CYP2D6, and CYP2C19 (Sugano, 2018). The reported metabolic pathways showed the removal or blocking of the active amino group in the VPZ parent molecules, therefore, these metabolites become electrically inactive. A In a pharmacokinetic and pharmacodynamic analysis of VPZ fumarate, it was discovered that 59% of VPZ was retained in urine as metabolites, with only 8% of the unchanged form remaining, suggesting comprehensive metabolism (Echizen, 2016).
3.7 Sample analysis
Known aliquots of the VPZ standard solution were spiked to the biological samples solution, transferred to the measuring cell where the VPZ content was assayed voltammetrically using the fabricated CuO/CPE at the optimum measuring parameters. The average recoveries were calculated and compared with those achieved by the HPLC method with UV detection at 230 nm (Table 2). SD = standard deviation; RSD = relative standard deviation, SE = standard error. bValues in parentheses are the theoretical values corresponding to t and F at P = 0.05.
Parameters
DPV
Reported HPLC Method (Luo et al., 2018)
Meana
100.05
100.01
SD
0.05
0.08
Variance
0.013
0.011
N
5
5
Student’s t-test (1.860)
0.62
F-test (6.39)
1.115
Urine sample
Taken (µg mL−1)
Found (µg mL−1)
bias
Recovery
HPLC
20
20.02
0.02
100.1
99.9
15
14.98
0.02
99.87
100.05
10
9.99
0.01
99.90
99.98
Mean
99.96
99.96
Variance
0.01
0.02
t Stat
0.249
t Critical two-tail
2.78
F
2.83
F Critical
19
Serum
Parameters
Taken
Found
bias
Recovery
HPLC
20
20.03
0.03
100.15
99.95
15
14.97
−0.03
99.80
100.16
10
10.02
0.02
100.20
99.97
Mean
100.05
100.03
Variance
0.05
0.01
Observations
3
3
t Stat
0.88
t Critical two-tail
2.78
F
3.54
F Critical
19
The adequacy of the proposed analysis methodology for analyzing VPZ in pure forms and biological samples in the presence or absence of phenylephrine was demonstrated by high recoveries and suitable relative standard deviation values (Table 2).
Comparing the performance of the proposed method with the published HPLC protocol (S3), the present method showed acceptable sensitivity and average recoveries with the advantages of fast low cost analysis.
4 Conclusion
For the first time, novel carbon paste sensors incorporated with copper oxide nanoparticles for sensitive differential pulse voltammetric determination VPZ in pure form and biological fluids. Copper oxide nanopowder offered the proper electrocatalytic effect toward the electrochemical oxidation of VPZ at the electrode surface with a diffusion-controlled reaction mechanism. The fabricated sensor showed improved sensitivity against VPZ within the concentration range from 0.99 to 20.00 µg mL−1 with LOD 0.24 µg mL−1. In addition, the simultaneous voltammetric determination of VPZ, AA, and UA was discussed with a parallel studying the effect of interferents and degradation products. The enhanced selectivity and sensitivity of the fabricated sensors suggesting their application for voltammetric assay of VPZ in pharmaceutical and biological samples compared with the conventional HPLC techniques.
Acknowledgment
This research was funded by the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Fast-track Research Funding Program.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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Appendix A
Supplementary material
Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2021.103254.
Appendix A
Supplementary material
The following are the Supplementary data to this article:
